A. High Capacity Output Stacking Trays
In the prior art of output trays there has generally been an association of large, complex and expensive high volume copiers with similarly large, complex and expensive high capacity output collecting devices such as elevator trays, collators, sorters, vertically repositionable sheet output ports, and “mailbox” systems. In part this is because high volume copiers often must be capable of being coupled to subsequent machines in a production line, requiring that the top of the output stack be maintained at a relatively precise elevation for pickup by the next machine in the production line. However, where subsequent processing is not necessary there has previously been no simple, inexpensive, high capacity output stacking tray system available as a final station for such high volume copiers which did not suffer from various drawbacks addressed by the present invention.
Similarly, there has been an association of smaller, slower, and less expensive copiers with small, fixed, limited capacity output trays. High capacity output trays or systems with elevators or multiple trays generally either been unavailable for such smaller machines, or are too expensive to be suitable for the typical uses of such machines.
In all types of document production machines such as copiers, printers and fax machines, but particularly copiers for high speed, high volume production runs, the production of sheets by the copier can often exceed the capacity of presently available output catch tray systems. High capacity output trays, often referred to in the art as “stackers,” are particularly desirable for the collected output of high speed or plural job batching copiers or printers. High capacity stackers are also desirable for the accumulated output of unattended plural user (networked) copiers and printers, of any speed.
Further by way of background on sheet stacking difficulties in general, outputted sheets are usually ejected into an output tray from above one side thereof. Normal output stacking is by ejecting sheets or sets of sheets from above one side of the top sheet of the stack of sheets onto which that additional ejected sheet or set of sheets must also stack. Typically, sheets or sets are ejected generally horizontally (or slightly uphill initially) and continue to move horizontally primarily by inertia. That is, sheets or sets in the process of being stacked are not typically effectively controlled or guided once they are released into the output tray. The sheets or sets fall by gravity into the tray to settle onto the top of the stack. However, such settling is resisted by the relatively high air resistance of the sheet or set to movement in that direction. Yet, for high volume copiers stacking must be done at high speed, so a long settling time is undesirable. Thus, a long drop onto the stack is undesirable.
Stacking is made even more difficult where there are variations in thickness, material, weight and condition (such as curls) of the sheets. Different sizes or types of sheets, such as tabbed or cover sheets or Z-folded or other inserts, may even be intermixed in the stack. The ejection trajectory and stacking should thus accommodate the varying aerodynamic characteristics of such various rapidly moving sheets or sets. A fast moving sheet or set can act as a variable airfoil to aerodynamically affect the rise or fall of the lead edge of the sheet as it is ejected. This airfoil effect can be strongly affected by curls induced in the sheet, by fusing, color printing, etc. Therefore, an upward trajectory output angle and substantial release height is often provided, well above the top of the stack. Otherwise, the lead edge of the entering document can catch or snub on the top of the stack already in the output tray, and curl over, causing a serious jam condition. However, setting too high a document ejection level to accommodate all these possible stacking problems greatly increases the settling time for all sheets or sets and creates other potential problems, such as scattering.
Scatter within a stack causes at least four problems. First, if copier has a sets offsetting feature, intended to provide job set separations or distinctions, scatter within a stack makes such set distinction more difficult. Second, misaligned sheets or sets tend to incur damage such as bending, folding, abrasion or tearing of sheet edges out of alignment with the overall stack edge. Third, a substantial stack within which individual sheets are not well aligned to each other is more difficult for an operator to grasp and remove from the stacker. Fourth, a misaligned stack is not easily loaded into a box or other transporting container of corresponding dimensions.
For the above listed reasons, it may be seen that the top of stack elevation should be maintained within a desired range. A tray elevator or vertically repositionable sheet output port is therefore normally provided to maintain a relatively constant relationship of sheet output elevation to top of stack elevation for high capacity output trays.
Numerous means for dealing with various such general problems of sheet stacking are taught in U.S. Pat. No. 4,385,758, U.S. Pat. No. 4,469,319, U.S. Pat. No. 5,005,821, U.S. Pat. No. 5,014,976, U.S. Pat. No. 5,014,977, U.S. Pat. No. 5,033,731, and art therein. Sheet “knock down” or settling assistance systems are known, but add cost and complexity and can undesirably prematurely deflect down the lead edge of the ejected sheet. Also, such “knock down” systems can interfere with sheet stack removal or loading and can be damaged thereby. Also, stacking systems should desirably provide relatively “open” trays, which will not interfere with open operator access to the output stacking tray or bin, for ease of removal of the sheet stack therein.
Many attempts have been made in the prior art to provide high capacity sheet stacking output trays. Among these are: U.S. Pat. No. 5,609,333 (describing a sheet stack height control system); U.S. Pat. No. 5,318,401 (describing a stacking tray system with nonvertically receding elevator yielding square stacks); U.S. Pat. No. 5,346,203 (describing a high capacity sheet stacking system with variable height input and stacking registration); U.S. Pat. No. 4,329,046 (describing a method for operating a reproduction machine with unlimited catch tray for multimode operation); U.S. Pat. No. 4,141,546 (describing a mini-collator/sorter); U.S. Pat. No. 4,012,032 (describing a sheet handling system with a receiving tray for use in non-collate mode and a plurality of collator bins for operating in collator mode); U.S. Pat. No. 4,026,543 (describing a control system using a copy count, a tangent copy count, and a document tracing indicator to provide automatic control for copy overflows); U.S. Pat. No. 4,134,581 (describing a system having multiple collator bins treated as one virtual bin.)
In these systems there are generally two approaches to increasing output catch tray capacity. The first approach uses multiple receipt trays, bins or mailboxes (for simplicity, collectively referred to as “trays). The trays may be vertically or horizontally repositionable relative to a fixed output port, or the copier output port may be vertically or horizontally repositionable relative to a fixed tray or trays, or some combination of movable trays and moveable output port may be employed. However, although though multiple trays are in use, the individual trays generally have limited capacities requiring either additional control for tray switching, system shutdown or additional operator intervention.
In the second approach a single large output catch tray is used, but relatively powerful, complicated and expensive elevator mechanisms are required either to lower the catch tray or raise the copier output port as the stack grows in order to keep the top of the stack within an acceptable range below the sheet output port. As far as is presently known, prior art does not include the combination of a single large output catch tray with a vertically repositionable output port.
Other systems such as U.S. Pat. No. 3,871,643 teach a sorter system having two sorter sections. In particular, the control switches from one section to the next to continue a copying job. Also, if the bins in both sections of the sorter contain copy sheets, and the job requirement has not been completed, upon removal of the copy sheets in one of the sections, the reproduction machine will resume operation after having been temporarily halted.
The addition of multiple bins and trays, catch trays with elevator mechanism, or vertically repositionable copier output port increases the complexity of the components for copiers and their controls, with a corresponding decrease in expected reliability and increase in cost. It would therefore be desirable to provide a high capacity output catch tray for document production machines such as photocopiers, printers and fax machines having a minimum number of receiving trays and/or complex mechanisms and yet be able to handle high volume requirements with minimum operator intervention. Due to the lack of such a device, it is not unknown in the prior art to use stacks of cardboard boxes as cheap, high capacity output “trays.”
B. Inclined Output Trays
For better stacking alignment to obtain neat, square and even-sided stacks, as is known in the art, it is preferable to output sheets or sets sequentially onto an inclined surface. Initially this is the inclined surface of the empty output tray, and then it is the correspondingly inclined upper surface of the sheet or set previously stacked thereon. If the output tray surface is upwardly inclined away from the copier output port into the tray, this is known in the art as “uphill” stacking. It is called “downhill” stacking if the output tray slopes downwardly away from the copier output port. There are many advantages to using either “uphill” or “downhill” stacking, either for stacking per se, or for stacking in a compiler for stapling or other binding or finishing. It allows different sizes of sheets to be stacked using the same paper path and the same tray system, using gravity assisted stacking against a simple inboard or outboard alignment surface, and is therefore relatively less expensive than more complicated active stacking registration or alignment systems, such as those requiring scullers, flappers, tampers, joggers, etc.
“Uphill” stacking desirably lends itself to stacking alignment at an inboard side of the output tray, that is, at the side adjacent the copier. It automatically slows down the ejected sheets, due to their initial “uphill” movement. The sheets then reverse their movement to slide back down against an upstanding wall or edge adjacent to but underlying the output port. Incoming sheets thus do not get caught on the edge of the stack in the tray, so long as subsequent sheets or sets enter above the top of the stack, which of course grows in length/height as the copy job progresses.
Prior art does not provide for a high capacity single output tray which can quickly and easily be configured to provide uphill, horizontal or downhill output stacking without the use of a tray elevator or vertically repositionable sheet output port.
C. Stack Edge Alignment
It is known in the art to provide a stacking system with an output tray elevator. The top of a stack in the output tray is maintained at a suitable height for such stacking, by the output tray and all its contents being moved downward as the stack accumulates, so that the top of the stack remains in the same general relative position below the copier output port.
In prior art, the stacking alignment surface is normally a fixed vertical surface which does not move relative to the copier and its output port, and not an integral upstanding side of the tray itself, as in a sorter bin or other conventional stacking tray. That is, the alignment surface against which the ejected sheets or sets are aligned is typically the vertical surface of the side of the machine or the stacking tray elevator itself, against which the sheets or sets may align as they stack.
In part, such a fixed alignment surface addresses the problem that if, instead, a conventional alignment side wall integral (and substantially perpendicular to) the stacking tray were provided (moving therewith), that alignment wall require a height equal to the full elevator travel range of the output tray. Otherwise, sheets or sets stacked higher than that alignment wall would slide off the stack. In the empty, fully raised position of such an output tray, such a fixed height alignment side wall would unacceptably extend well above the top of the machine, and/or block the sheet entrance to the tray if located on that side of the tray for “uphill” stacking.
Also, with such an output tray designed for high capacity stacking, the first incoming sheets would be required to drop a substantial distance before coming to rest on the top of the stack or tray. This large drop distance tends to increase the number of stacking problems noted above, such as sheets or sets coming to rest in an orientation other than flat against the top of the stack, and/or substantial scatter within the stack.
However, previous systems with fixed alignment surfaces suffer from various drawbacks. Since the edges of the sheets in the stack move relative to the alignment surface, friction of the sheet edges against the alignment surface lifts the sheet edges relative to the downward motion of the output tray, abrading the sheet edges and disturbing the stack so that is less flat, neat and square. This phenomenon is known in the art as “creep.” With the extended use experienced by high volume copiers, over time, the friction also causes wear on the alignment surface so that it may become less smooth, exacerbating the problems of lift and creep. Fixed alignment surfaces must also be relatively long to provide high capacity and are therefore relatively bulky.
One previous attempt to deal with the problem of fixed alignment surfaces can be seen in U.S. Pat. No. 5,346,203, in which a variable height stack registration and edge alignment system is provided by way of numerous small belt-like flexible sheets which unroll upward corresponding to upward movement of a vertically repositionable sheet output port. However, as with previous tray elevator systems, this system is subject to the drawbacks of complexity, expense, and limited inter-connectivity; even more so in that it is associated with multiple output tray and/or mailbox systems.
It is therefore desirable to provide a simple, relatively smooth, variable length stack alignment and edge alignment system which corresponds directly and automatically to the output tray height and requires no external power source or control system.
To recapitulate, the limitations of the prior art of high capacity output trays are substantial. A simple fixed high capacity output tray without a vertically repositionable sheet output port is impractical because it requires either a high fixed side wall or that the output tray be very deep, so that ejected sheets or sets would have too far to drop and be subject to the abovementioned problems of scatter, disorientation, buckling, folding, etc. Vertically repositionable copier output ports, output tray elevators, multiple trays/bins/mailboxes are all relatively complex and high maintenance, require external power sources and controls, and are correspondingly expensive both initially and over time.
The present invention provides a simple, high capacity, adjustable, sheet stacking output tray suitable for connection to both large, high volume copiers and to smaller, less expensive ones, which is capable of automatically maintaining the top of stack height within an acceptable range relative to the sheet output port, without external power source or control, where precise stack height control is not required. The various adjustments in output tray angle, stack angle, effective spring rate, total weight capacity, and total stack height permitted by the invention allow a user to customize and optimize the invention for numerous applications. The invention thus uniquely provides for maximum upgrade-ability, downgrade-ability and compatibility between various sizes, types and brands of document production devices.